To the author’s knowledge, this is the first systematic study of the concept of enmity in the political philosophy of Thomas Hobbes. Examining this important category does not only elucidate the concept itself, but also provides an opportunity to reconnect fragments of Hobbes’s thought that are increasingly being treated as disparate subjects. It is suggested that the notion of enmity can shed further light on related aspects of his political philosophy, including human competitiveness, the roles of fear and trust, the evil of violent death, the status of rebels, and his theory of international relations. In addition, the subject invites a rethinking of Hobbes’s place in the history of political thought. It is argued that he was among the first to make enmity a central subject of political philosophy. This seems to be related to Hobbes’s break with the traditional notion of natural sociability, as a consequence of which he describes the natural condition of mankind as a war of all against all. Although Hobbes depicts human beings as natural enemies, he holds that enmity does not exclude the possibility of reconciliation; individuals can supposedly overcome their hostility through subjection to a sovereign. These views give rise to a dynamic distinction between public and private enmity, according to which outright hostility can be transformed into private rivalry if human beings renounce their natural right of war. Conversely, subjects become public enemies if they rebel against the sovereign. Hobbes’s views on natural enmity and reconciliation also have important implications for his theory of international relations. This thesis particularly highlights the possibility that states can be decomposed and reassembled after a foreign invasion, which precludes wars of annihilation.